It began in 2007 with a few traders in the small town of Modbury in Devon refusing to give out plastic bags. But yesterday their small green revolution reached a national milestone: British shoppers have nearly halved the number of single-use bags they get through.

Figures from Wrap, the government's waste and resources programme, show that whereas 870m single-use plastic bags were handed out in the UK in May 2006, the figure for May 2009 was down to 450m – a 48% reduction, and 4,740 tonnes to send to landfill against 8,890 tonnes in May 2006.

Nationwide rejection of the bags, which take up to 1,000 years to decompose and clog drains and pollute oceans, followed a government challenge to retailers to voluntarily halve bag use by June 2009.

"Over the past year or so, we've invested £3m to help our customers change the habit of a lifetime. We've cut the number of single-use bags our customers use by 53%," said an Asda spokeswoman.

But Asda still expressed frustration at the scheme. "The populist appeal of plastic bags has obscured more pressing issues, such as packaging reduction, carbon and energy use, and waste."

Further reductions should be implemented through a carrot not a stick approach, and at retailers' own discretion, it said. The €0.15 (12p) tax introduced in the Republic of Ireland in 2002 has cut bag use by more than 90%.

Yesterday the Welsh Assembly government said the dramatic reduction in bag use would not affect its proposal to introduce a 15p charge on single-use carrier bags. "Wales is still using 27m plastic bags a month, or 324m a year, " said the environment minister Joan Davidson.

Rebecca Hosking, the BBC filmmaker who persuaded Modbury and other towns to reject plastic bags after seeing how they killed wildlife around the world, yesterday said the supermarkets had fought hard against the voluntary reduction in bag use. "What has been achieved is fantastic but they have complained non-stop like little children. You'd have thought they were being asked to go on a vegan diet or something. This has not been difficult at all. No-one has lost trade, or gone out of business in Modbury or anywhere else," she said.

The plastic bag issue has divided environmentalists with some arguing the action is inconsequential while others say it is an important symbol of reduced consupmtion and often leads to further environmental action.